Container for electromagnetic cookers

ABSTRACT

[Problem] To provide a container for an electromagnetic cooker which can be heated corresponding to impedance check frequency which differs depending on a manufacturer of an electromagnetic cooker or the like, can properly and easily set a heat generation characteristic, is excellent in marketability, configuration in use, disposability, handiness in cooking and the like, is suitable for retort foods, instant foods and the like, and exhibits high heating efficiency. 
     [Means for Resolution] A container for an electromagnetic cooker includes a container body made of a non-conductive material and a conductive layer in a bottom portion of the container, wherein the ratio of resistance change (R−R 0 )/R 0  of the conductive layer with respect to the impedance check frequency of a heating coil is set to 5.3 or more, and a ratio of inductance change (L−L 0 )/L 0  of the conductive layer with respect to the impedance check frequency of the heating coil is set to −0.17 or less. Here, R indicates the high-frequency resistance (Ω) on a heating coil side with a load, R 0  indicates the high-frequency resistance (Ω) on the heating coil side without a load, L indicates the inductance (μH) on the heating coil side with a load, and L 0  indicates the inductance (μH) on the heating coil side without a load.

TECHNICAL FIELD

The present invention relates to a container for an electromagneticcooker which can heat a content using Joule heat which is generated byan eddy current induced by an electromagnetic induction coil of theelectromagnetic cooker.

BACKGROUND ART

Recently, an electromagnetic cooker which does not generate flames hasbeen used in a household, a place that serves food and drink such as arestaurant or the like for cooking foods or heating cooked foods from aviewpoint of safety, cleanliness, convenience and economy. Theelectromagnetic cooker heats food in a container such that, when acontainer for an electromagnetic cooker made of steel or stainless steelis placed on the electromagnetic cooker, an eddy current is generated ina bottom portion of the container for an electromagnetic cooker due tolines of magnetic force from an electromagnetic coil, and this eddycurrent induces Joule heat which is used for heating the food in thecontainer.

Further, by making use of such a principle, a large number ofelectromagnetic induction rice cooker (IH rice cookers) has beencommercialized. As an instant-food-use container which enables heatingthereof using an electromagnetic cooker by making use of such aprinciple, there has been proposed a container for an electromagneticcooker such as an instant-food-use container which enables directheating of a container which packs noodles such as Chinese noodles,buckwheat noodles or Japanese noodles, fried noodles therein by anelectromagnetic cooker (patent document 1) or an aluminum-foil-made foodcontainer which enables heating of a container by an electromagneticcooker (patent document 2).

Still further, there have been also proposed a container which is usedin common for an electromagnetic cooker and an microwave oven and ismanufactured by taking the separation of parts of the container bykinds, incineration of the container and recycling of a magnetic bodywhich constitutes a heat generating body after use into consideration(patent document 3) and a container for an electromagnetic cooker whichallows an aluminum foil to generate heat (patent document 4).

[Patent document 1] JP-A-2000-272676[Patent document 2] JP-A-2002-51906[Patent document 3] JP-A-2002-177149[Patent document 4] JP-A-2003-325327

DISCLOSURE OF THE INVENTION Task to be Solved by the Invention

However, in heating the instant-food-use containers by the conventionalelectromagnetic cooker described in the above-mentioned patent documentsor the like, the instant-food-containers have following drawbacks.

The instant-food-container described in patent document 1 is constitutedof an inner-layer container formed of a steel plate and an outer-layercontainer made of an insulation material. This patent document 1 furtherproposes following technical features. That is, a bottom surface of theinner-layer container is positioned within 5 mm from a bottom surface ofthe outer-layer container, a thickness of the steel plate is set to avalue which falls within a range from 0.05 to 0.5 mm, and at least oneor more processing selected from plating, chemical conversion treatment,lamination of a resin film and painting is applied to one or bothsurfaces of the steel plate from a viewpoint of imparting corrosionresistance to the instant-food-container. However, to take the fact thatthe instant-food-container is used for an instant food intoconsideration, such constitution pushes up a material cost and a formingcost and hence, the container is not economical. Further, with respectto impedance check frequency for determining whether or not anelectromagnetic cooker can be heated, it is difficult to adjust athickness or the configuration of a heat generating body, a distancefrom a heating coil or the like and hence, it is difficult to properlyand easily set the heat generation properties.

Here, the impedance check frequency is frequency which is used fordetermining whether or not an electromagnetic cooker can be heated anddiffers from frequency at the time of actually heating theelectromagnetic cooker. Further, a method for determining whether or notan electromagnetic cooker can be heated differs among manufacturers ofelectromagnetic cookers and hence, the impedance check frequency alsodiffers depending on the manufacturers of electromagnetic cookers.

Further, with respect to the container described in patent document 2,there is proposed an aluminum-foil material-made food container whichcan be heated by an electromagnetic cooker, wherein the container has aflat bottom surface and is made of an aluminum foil material having athickness of 12 μm to 96 μm. However, it is difficult for such a foodcontainer to adjust a thickness, the configuration or the like of theheat generating body corresponding to an oscillation conditions of anelectromagnetic cooker (impedance check frequency intrinsic to amanufacturer) or the like and hence, it is difficult to properly andeasily set heat generation properties.

Further, with respect to the container described in patent document 3,there has been proposed a container which mounts a plate material (heatgenerating body) formed of a magnetic body on a recessed bottom surfaceof a container made of a non-magnetic material, and the heat generatingbody is made of ferrite-based stainless steel or a material similar tothe ferrite-based stainless steel. This kind of container pushes up amaterial cost and a forming cost when used for an instant food andhence, the container is not economical. Further, it is difficult toadjust a thickness or the configuration of a heat generating body, adistance from a heating coil or the like corresponding to oscillationconditions of an electromagnetic cooker (impedance check frequencyintrinsic to a manufacturer) or the like and hence, it is difficult toproperly and easily set the heat generation properties.

Further, with respect to the container described in patent document 4,there is proposed a technique in which an aluminum foil having athickness of 0.10 to 100 μm is mounted on a bottom portion of anon-magnetic container body as a heat generating body, and the bottomportion of the container body has a thickness of 12.0 mm or lessmeasured from a mounting surface of an electromagnetic cooker. Even whenthe electromagnetic cooker is manufactured under such conditions, theremay be a case that a manufacturer of an electromagnetic cooker changesan oscillation conditions (impedance check frequency intrinsic to themanufacturer). In such a case, with mere setting of such conditions, itis impossible for an electromagnetic cooker to heat the container.

The present invention has been made to overcome the above-mentioneddrawbacks, and it is an object of the present invention to provide acontainer for an electromagnetic cooker which is suitable for retortfoods, instant foods or the like and exhibits high heating efficiency.The container can be manufactured at a low material cost and at a lowforming cost as an instant-food-use container for heating food using anelectromagnetic cooker. The container can be heated corresponding to theoscillation conditions of electromagnetic cookers which differ forrespective manufactures (impedance check frequencies intrinsic to themanufacturers) or the like. The container also can properly and easilyset a shape and heat generation properties of the containercorresponding to a using purpose of the container.

Task to be Solved by the Invention

A container for an electromagnetic cooker described in claim 1 accordingto the present invention is characterized in that the container for theelectromagnetic cooker includes a conductive layer at least in a bottomportion of the container made of a non-conductive material, wherein theratio of resistance change (R−R0)/R0 of the conductive layer withrespect to the impedance check frequency of a heating coil is set to 5.3or more, and the ratio of inductance change (L−L0)/L0 of the conductivelayer with respect to the impedance check frequency of the heating coilis set to −0.17 or less. Here, R indicates the high-frequency resistance(Ω) on a heating coil side with a load, R0 indicates the high-frequencyresistance (Ω) on the heating coil side without a load, L indicates theinductance (μH) on the heating coil side with a load, and L0 indicatesthe inductance (μH) on the heating coil side without a load.

The container for the electromagnetic cooker described in claim 2 is, inthe constitution described in claim 1, characterized in that theconductive layer is formed of a metal foil.

The container for the electromagnetic cooker described in claim 3 is, inthe constitution described in claim 1, characterized in that theconductive layer is formed of a coating material containing metalpowder.

The container for the electromagnetic cooker described in claim 4 is, inthe constitution described in any one of claims 1 to 3, characterized inthat the conductive layer is formed on an inner surface of the bottomportion of the container.

The container for the electromagnetic cooker described in claim 5 is, inthe constitution described in claim 4, characterized in that theconductive layer is made of a laminate material constituted of aconductive material and a non-conductive material, and the conductivematerial is disposed on a bottom-portion side of the container.

The container for the electromagnetic cooker described in claim 6 is, inthe constitution described in any one of claims 1 to 5, characterized inthat the non-conductive material of the conductive layer is curvedupwardly along a side wall of the container, and is adhered to a lowerportion of an inner surface of the side wall of the container.

The container for the electromagnetic cooker described in claim 7 is, inthe constitution described in claim 5 or 6, characterized in that acontent liquid convection hole is formed in the non-conductive materialof the laminate material.

The container for the electromagnetic cooker described in claim 8 is, inthe constitution described in any one of claims 1 to 7, characterized inthat the conductive layer is formed into a doughnut shape.

The container for the electromagnetic cooker described in claim 9 is, inthe constitution described in any one of claims 1 to 8, characterized inthat the conductive material of the conductive layer is formed into anuneven shape for increasing a surface area of the conductive material.

The container for the electromagnetic cooker described in claim 10 is,in the constitution described in any one of claims 7 to 9, characterizedin that the conductive layer is configured to be vertically movable.

The container for the electromagnetic cooker described in claim 11 is,in the constitution described in any one of claims 1 to 10,characterized in that the conductive material is formed by lamination.

The container for the electromagnetic cooker described in claim 12 is,in the constitution described in claim 11, characterized in that theconductive material is formed by lamination while preventing endportions of the conductive material from overlapping with each other.

ADVANTAGE OF THE INVENTION

According to the container for an electromagnetic cooker of the presentinvention, the container can be heated corresponding to the oscillationconditions (impedance check frequency intrinsic to the manufacturer) ofthe electromagnetic cooker which differs for respective manufacturesand, at the same time, the heat generation properties of the containercan be properly and easily set thus enabling the acquisition of theelectromagnetic cooker having high heating efficiency suitable forretort foods, instant foods and the like at a low cost.

Further, it is possible to provide the container for an electromagneticcooker which is excellent in marketability, configuration in use,disposability, handiness in cooking and the like.

BEST MODE FOR CARRYING OUT THE INVENTION

A container for an electromagnetic cooker according to the presentinvention is characterized by including a conductive layer at least in abottom portion of the container made of a non-conductive material,wherein the ratio of resistance change (R−R0)/R0 of the conductive layerwith respect to the impedance check frequency of a heating coil is setto 5.3 or more, and the ratio of inductance change (L−L0)/L0 of theconductive layer with respect to the impedance check frequency of theheating coil is set to −0.17 or less. Here, R indicates thehigh-frequency resistance (Ω) on a heating coil side with a load, R0indicates the high-frequency resistance (Ω) on the heating coil sidewithout a load, L indicates the inductance (μH) on the heating coil sidewith a load, and L0 indicates the inductance (μH) on the heating coilside without a load.

In the present invention, the reason that the property of the conductivelayer is specified using the ratio of resistance change and the ratio ofinductance change is as follows. When the number of kinds of theelectromagnetic cookers is only one, the property of the conductivelayer can be acquired using a change quantity of the high-frequencyresistance R (Ω) and a change quantity of the inductance L (μH).However, a heating coil differs for every manufacturer of anelectromagnetic cooker or for every type of electromagnetic cooker andhence, the high-frequency resistance R0 (Ω) on the heating coil sidewithout a load and the inductance L0 (μH) on the heating coil sidewithout a load differ for every manufacturer or for every type ofelectromagnetic cooker. Accordingly, the property of the conductivelayer is acquired by calculating the change ratio of the high-frequencyresistance (Ω) R and the change ratio of the inductance (μH) L.

The electromagnetic cooker utilizes the cancellation of magnetic fluxesby an AC current and the heat generation principle based on an eddycurrent which flows in a conductive body, and an oscillating frequencyof the current is set to 10 to 90 kHz in general. On the other hand, asa material of a cooking container of the electromagnetic cooker, aferromagnetic body which has a suitable thickness and can cancel ACmagnetic fluxes is used. That is, a steel-made pan and the like made ofiron having the proper electric resistance and a proper containerstrength is used as the cooking container.

Further, inventors of the present invention have extensively carried outexperiments using electromagnetic cookers manufactured by variousmanufacturers and, as a result of the experiments, have found that withthe use of the container in which a conductive material for constitutinga conductive layer exhibits the ratio of resistance change (R−R0)/R0 ofthe conductive layer with respect to the oscillation condition of theelectromagnetic cooker of each manufacturer (impedance check frequencyintrinsic to the manufacturer) which is set to 5.3 or more, and theratio of inductance change (L−L0)/L0 of the conductive layer withrespect to the oscillation condition of the electromagnetic cooker ofthe respective manufacturers (impedance check frequency) which is set to−0.17 or less, that is, with the use of the container in which theconductive material which forms the conductive layer of the bottomportion of the container satisfies the above-mentioned change ratios,the cooking container can be heated corresponding to the electromagneticcooker of each manufacturer. Further, although the smallest diameter ofa pan of each manufacturer which can be heated is 120 mm, by adjustingproperties of the conductive layer to satisfy the above-mentioned changeratios, it is possible to further decrease a value of the smallestdiameter of the container.

First of all, the ratio of resistance change and the ratio of inductancechange according to the present invention are explained. FIG. 1 is anexplanatory view showing a method of measuring the high-frequencyresistance and the inductance using an impedance analyzer.

As shown in FIG. 1, with respect to various kinds of conductivematerials each of which is mounted on a bottom portion of the containeras a conductive layer, each conductive material is placed on a top plateof the electromagnetic cooker manufactured by each manufacturer, and thehigh-frequency resistance R and the inductance L with respect to theimpedance check frequency on a heating coil side are measured using theimpedance analyzer. Next, the ratio of resistance change is defined as(R−R0)/R0, and the ratio of inductance change is defined as (L−L0)/L0.Here, R0 indicates the high-frequency resistance (Ω) on the heating coilside without placing anything on the top plate, and L0 indicates theinductance (μH) on the heating coil side without placing anything on thetop plate.

FIG. 2 shows a result of confirmation whether or not the respectiveconductive materials can be heated at the impedance check frequency in astate that each one of various kinds of conductive materials is placedon the top plate of the electromagnetic cooker of each manufacturer inthe above-mentioned manner. The result also includes a result of theratio of resistance change and the ratio of inductance change in such aconfirmation operation.

In FIG. 2, the conductive materials which can be heated are indicated byoutlined symbols. As shown in FIG. 2, it is found that there exists arange within which the conductive materials can be heated regardless ofthe electromagnetic cookers manufactured by the respectivemanufacturers. It is also found that the conductive materials can beheated by the electromagnetic cookers manufactured by the respectivemanufactures provided that the above-mentioned ratio of resistancechange (R−R0)/R0 is set to 5.3 or more, and the above-mentioned ratio ofinductance change (L−L0)/L0 is set to −0.17 or less.

In general, there exists a tendency that when a thickness of the foil ofthe conductive layer is increased, the change ratio of the inductance L(μH) is decreased, the high-frequency resistance (Ω) R is decreased.Further, when the thickness of the foil of the conductive layer isincreased, the ratio of inductance change (L−L0)/L0 is increased in thenegative direction, and the ratio of resistance change (R−R0)/R0 isdecreased.

Here, a thickness, a size, configuration, a material of the conductivelayer may de determined within a range of the above-mentioned changeratios (the ratio of resistance change being set to 5.3 or more, and theratio of inductance change being set to −0.17 or less).

Next, FIG. 3 shows the relationship between a material of the conductivelayer and a required thickness of the conductive layer within theabove-mentioned change ratios. FIG. 3 shows in an exemplified manner aresult obtained by an experiment on the relationship between the bulkspecific resistances of respective conductive materials and foilthicknesses of metal foils consisting of a silver foil, an aluminum foiland a tin foil necessary for heating. In the experiment, the conductivematerial is heated by an electromagnetic cooker (KZ-PH1) made byMATSUSHITA ELECTRIC INDUSTRY Co., Ltd. and a smallest diameter of theconductive material is set to φ85 mm.

It is understood from the result of the experiment that when the bulkspecific resistance of the conductive material is small, it issufficient for the conductive material to have a small thickness, whilewhen the bulk specific resistance of the conductive material is large,it is necessary to increase the thickness of the conductive material.Here, the bulk specific resistance is resistivity intrinsic to amaterial and means volumetric resistivity.

As the non-conductive material which forms a container body of thecontainer for an electromagnetic cooker of the present invention, it ispossible to use a multi-layered material which forms an intermediatelayer thereof using a gas-barrier resin such as an olefin resin selectedfrom a group consisting of polyurethane, polyethylene, polypropylene andthe like, a polyester resin, a polyamide resin, or ethylene-vinylalcohol copolymer.

Further, the container body may be formed using paper or a multi-layeredmaterial consisting of paper material and the above-mentioned resin.

Still further, the container may be configured in a cup shape, a trayshape, a standing pouch shape or the like. However, the configuration ofthe container is not limited to such shapes.

The conductive layer is preferably formed using a metal foil from a viewpoint that the ratio of inductance change can be satisfied, and it isalso preferable to laminate the metal foils having a thickness as smallas possible from a viewpoint that the ratio of resistance change can besatisfied. Such a metal foil is not particularly limited. The conductivelayer may be made of either one of a magnetic material and anon-magnetic material. As the material of the conductive layer, a silverfoil, a gold foil, a copper foil, a platinum foil, an aluminum foil, azinc foil, a tin foil, a nickel foil, an iron foil, a stainless steelfoil and the like may be named. The aluminum foil is more preferablefrom a viewpoint of a manufacturing cost. Here, a laminate materialwhich is formed by laminating the metal foil of the conductive materialto a non-conductive material such as a sheet of paper or a resin sheetmay be mounted at least on an inner surface of a bottom portion of thecontainer. The laminate material may be mounted on the bottom portion ora side wall of the container.

With respect to the conductive material, when the gold foil, the silverfoil or the platinum foil is used as the metal foil, such a foil ishardly dissolved into food and hence, it is not always necessary to usethe foil in a form of a laminate material.

Further, from a viewpoint of increasing the high-frequency resistance,it is preferable to form the conductive layer by applying a coatingmaterial containing metal powder made of a conductive material such as aconductive paint to a bottom portion of the container, preferably to aninner surface of the bottom portion of the container. Here, the metalfoil is mounted on the bottom of the container and, thereafter, thecoating material made of the above-mentioned conductive material isapplied to the non-conductive material such as a sheet of paper or aresin sheet by coating thus forming the conductive layer on the bottomportion of the container.

In the container for an electromagnetic cooker of the present invention,although the conductive layer may be formed on an outer surface of thebottom portion of the container, from a viewpoint of preventing breakingof the container at the time of generation of heat or the like, it ispreferable to form the conductive layer on the inner surface of thebottom portion of the container. Further, from a viewpoint of enhancinga heat generation effect acquired by an eddy current which flows in theconductive material, it is preferable to form the conductive layer usinga laminate material made of a conductive material and a non-conductivematerial and to form the conductive material on a container bottomportion side.

Further, in the container for the electromagnetic cooker of the presentinvention, an end portion of the non-conductive material of theconductive layer formed of the laminate material may be curved upwardlyalong a sidewall of the container, and the end portion is adhered to alower portion of an inner surface of the side wall of the containerusing an adhesive agent or by heat sealing or the like thus facilitatingmounting of the conductive layer on the bottom portion of the container.

Further, by forming content liquid convection holes in theabove-mentioned non-conductive material, the convection of the liquidcan be effectively generated in the container at the time of heating thecontainer by the electromagnetic cooker. Further, by forming theabove-mentioned conductive layer in a donut shape, the heatingefficiency by the electromagnetic cooker can be enhanced. Still further,when the conductive layer is abnormally heated, the conductive layer isbroken so that heating can be stopped.

Further, by increasing a surface area of the conductive material of theconductive layer by forming unevenness on a surface of the conductivematerial, the heating efficiency can be further enhanced.

Further, in the container for an electromagnetic cooker of the presentinvention, by allowing the conductive layer to move upwardly anddownwardly, the conductive material of the conductive layer can be movedupwardly or downwardly from a heating coil of an electromagnetic cookerwithin a fixed range and hence, it is possible to prevent the containerfrom being damaged due to overheating of the conductive layer thusmaintaining the temperature of a content within a fixed range.

Further, when a thickness of the conductive material is sufficientlysmall compared to a penetration depth of a high-frequency current, theconductive material may have the multi-layered structure so that thehigh-frequency resistance and inductance can be adjusted within a properrange by adjusting the number of laminated layers whereby the heatingefficiency can be enhanced and, at the same time, a size of thecontainer can be set to a small size thus providing a compact container.In this case, from a viewpoint of preventing breaking of the containerby overheating, it is preferable to laminate layers of the conductivematerial such that end portions of the laminated layers do not overlapwith each other.

The container for an electromagnetic cooker according to the presentinvention is also applicable to an electromagnetic rice cooker (IH ricecooker). Further, by applying the conductive layer to the container bycoating such that a peripheral end portion of the conductive layer isnot exposed, it is possible to prevent a spark even when the containeris heated using by a microwave oven and hence, the container for anelectromagnetic cooker can be also used as a heating container for amicrowave oven.

The container for an electromagnetic cooker of the present invention isexplained in detail hereinafter in conjunction with attached drawings.

FIG. 4 and FIG. 5 show an embodiment 1 of the container for anelectromagnetic cooker of the present invention, wherein FIG. 4 is aplan view of the container and FIG. 5 is a cross-sectional view takenalong a line A-A in FIG. 4. Polypropylene (non-conductive material) isused as a material of the container 1. The container 1 has a side wallportion 2 and a bottom portion 3. A conductive layer 4 which is formedof a laminate material consisting of a conductive material 5 formed of aplurality of aluminum foils and a non-conductive material 6 made ofpolypropylene is formed on an inner surface of the bottom portion 3. Toposition the above-mentioned conductive material 5 on a bottom portion 3side of the container 1, an end portion of the non-conductive material 6of the conductive layer 4 is curved upwardly along the side wall 2 ofthe container 1, and the above-mentioned conductive layer 4 is mountedon a lower portion of the inner surface of the above-mentioned side wall2 by heat sealing.

Then, to effectively generate the convection of a liquid in thecontainer 1 at the time of heating by an electromagnetic cooker, contentliquid convection holes 7 are formed in the non-conductive material 6 ofthe above-mentioned laminate material which constitutes the conductivelayer 4.

Further, the above-mentioned conductive layer 4 is formed in a donutshape by forming a hole 8 in center portions of the conductive material5 and the non-conductive material 6 respectively and by removing suchcenter portions. Due to such constitution, the heating efficiency by theelectromagnetic cooker can be enhanced and, at the same time, even whenthe conductive layer 4 is abnormally heated, it is possible to preventoverheating caused by breaking of the conductive layer 4.

FIG. 6 to FIG. 9 show an embodiment 2 of the container for theelectromagnetic cooker of the present invention, wherein FIG. 6 is aplan view of the container, and FIG. 7 is a cross-sectional view takenalong a line B-B in FIG. 6. FIG. 8 and FIG. 9 show an inner cup(conductive material 5) which is mounted on an inner side of thecontainer of the embodiment 2, wherein FIG. 8 is a plan view of theinner cup and FIG. 9 is a front view of the inner cup.

As shown in FIG. 6 and FIG. 7, an inner cup fixing member is formed onthe container 1 such that an upper end portion of the inner cup fixingmember 9 is heat-sealed to an upper portion of the side wall 2 andfixing portions which project inwardly are formed on a side wall of theinner cup fixing member 9 at equal intervals. With the use of thisfixing member 9, it is possible to easily mount and fix an inner cup(conductive material 5) to the container 1. That is, it is possible tohouse the inner cup in the container 1 by arranging a conductive layer 4close to a bottom portion 3 of the container 1 and by inserting thefixing portions of the fixing member 9 into flared recessed portions 5 b(see FIG. 9) formed on a side wall 5 a of a conductive layer 4.

Here, with respect to the inner cup used in the container of theembodiment 2, as shown in FIG. 8 and FIG. 9, the conductive layer 4 iscurved upwardly such that the conductive material forming a lowersurface of the conductive material 5 formed of a plurality of aluminumfoils extends along the side wall 2 of the container 1, andvertically-elongated recessed portions 5 b are formed on the side wall 5a of the container 1 thus forming unevenness (wrinkles) at equalintervals thus increasing a surface area of the side wall 5 a wherebyheating efficiency can be further enhanced.

FIG. 10 to FIG. 12 show an embodiment 3 of the container for anelectromagnetic cooker according to the present invention, wherein FIG.10 is a plan view of the container, and FIG. 11 is a cross-sectionalview taken along a line C-C in FIG. 10. The container according to theembodiment 3 is formed such that a conductive layer 4 is formed of alaminate sheet material consisting of a donut-shaped conductive material5 formed of an aluminum foil and a non-conductive material 6 made ofpolypropylene which forms content liquid convection holes 7 therein in agrating shape. An annular leg portion 10 made of polypropylene issuitably adhered to a lower portion of a periphery of the conductivelayer 4 and is placed on an inner surface of a bottom portion 3 of acontainer 1 such that the conductive material 5 is arranged on acontainer bottom 3 side.

Due to such constitution, it is possible to easily steam the content inthe container.

Further, FIG. 12 shows a container for an electromagnetic cooker inwhich the conductive layer 4 is made light-weighted by removing theabove-mentioned leg portion 10. That is, in FIG. 12, the conductivelayer 4 is shown in a state that the conductive layer floats on acontent liquid. By allowing the conductive layer 4 to be movableupwardly and downwardly, the conductive material 5 of theabove-mentioned conductive layer 4 can be moved upwardly and downwardlywithin a fixed range from a heating coil of an electromagnetic cooker sothat it is possible to prevent the container from being damaged byoverheating of the conductive layer and it is also possible to maintaina temperature of the content within a fixed range.

Here, according to the container for an electromagnetic cooker of thepresent invention explained above, the conductive material 5 of theconductive layer 4 has the laminated structure and hence, it is possibleto adjust the high-frequency resistance and inductance such that theseproperties fall within proper ranges whereby the heating efficiency isenhanced and, at the same time, it is possible to make the container 1small-sized. Accordingly, it is possible to provide the container 1 of asize smaller than the smallest diameters of pans which the cookersmanufactured by the respective manufacturers can heat.

In this case, from a viewpoint of preventing breaking of the containerby overheating, it is desirable to laminate the foils such that endportions of the foils do not overlap with each other.

Further, when a thickness of the conductive material is sufficientlysmaller than a penetration depth, the conductive material may have themulti-layered structure and the high-frequency resistance and inductancemay be adjusted to values which fall within proper ranges by changingthe number of lamination layers.

Experiment

1. Measurement of high-frequency resistance (Ω) and inductance (μH) atimpedance check frequency of electromagnetic cooker and impedance checkfrequency of container for electromagnetic cooker, and calculation ofratio of resistance change and ratio of inductance change.

As shown in FIG. 1, using an LF•Impedance analyzer (4192A) made byYokogawa Hewlett Packard Co., high-frequency resistance R (Ω) andinductance L (μH) at the impedance check frequency of the conductivelayer of the manufactured container for an electromagnetic cooker aremeasured.

R0 indicates the high-frequency resistance (Ω) on the heating coil sidewithout placing anything on the top plate, and L0 indicates theinductance (μH) on the heating coil side without placing anything on thetop plate. The ratio of resistance change is calculated as (R−R0)/R0,and the ratio of inductance change is calculated as (L−L0)/L0.

2. Evaluation

400 cc of water is filled in the manufactured container for anelectromagnetic cooker, and the container is heated by theelectromagnetic cookers and the IH rice cookers manufactured by therespective manufacturers, and it is confirmed whether or not thecontainer can be heated by the electromagnetic cookers and the IH ricecookers manufactured by all manufacturers. With respect to theelectromagnetic cookers with which the container can be heated, thetemperature elevation time from 30° C. to 80° C. is measured.

(Experiment 1)

A container body having an inner diameter of 175 mm, a height of 120 mmand an inner volume of 1200 cc is formed using a polypropylene sheethaving a thickness of 2.5 mm.

On the other hand, a conductive material is formed by laminating twoaluminum foils having a thickness of 7 μm and an outer diameter of 150mm, and a polypropylene film is laminated to both surfaces of theconductive material thus forming a conductive layer.

Then, an end portion of the polypropylene film is heat-sealed to a lowerportion of an inner surface of a side wall of the container body suchthat the aluminum foils which constitute the conductive material arepositioned on a bottom portion side of the container body in thecontainer body thus forming a container for an electromagnetic cooker.

The container is heated using four kinds of electromagnetic cookers,that is, KZ-PH1 made by MATSUSHITA ELECTRIC IND CO LTD, MH-B1 made byHitachi Home & Life Solutions, Inc., IC-SF10 made by SANYO Electric Co.,Ltd. and MR-A25LH made by TOSHIBA CONSUMER MARKETING CORPORATION, and itis evaluated whether or not the container can be heated by therespective electromagnetic cookers.

(Experiment 2)

Heating of a container for an electromagnetic cooker and evaluation onwhether or not the container can be heated by electromagnetic cookersare performed in the same manner as the experiment 1 except for that ahole having a diameter of 60 mm is formed in a center portion of theconductive layer of the experiment 1 thus forming the conductive layerinto a donut shape.

(Experiment 3)

A container body having an inner diameter of 110 mm, a height of 50 mmand an inner volume of 600 cc is formed using a polypropylene sheethaving a thickness of 0.5 mm.

On the other hand, a conductive material is formed by laminating threealuminum foils having a thickness of 7 μm and an outer diameters of 110mm, 105 mm and 100 mm, a polypropylene film is laminated to bothsurfaces of the conductive material, and a hole having a diameter of 60mm is formed in a center portion of the polypropylene film thus forminga conductive layer.

Then, an end portion of the polypropylene film is heat-sealed to a lowerportion of an inner surface of a side wall of the container body suchthat the conductive material of the conductive layer is positioned on abottom portion side of the container body in the container body thusforming a container for an electromagnetic cooker. Thereafter, heatingof a container for an electromagnetic cooker and evaluation of whetheror not the container can be heated by electromagnetic cookers areperformed.

(Experiment 4)

In this experiment 4, it is confirmed whether or not the container foran electromagnetic cooker of the experiment 1 can cook rice using IHrice cookers. As the IH rice cookers, seven kinds of rice cookers, thatis, SR-XG10 made by MATSUSHITA ELECTRIC IND CO LTD, ECJ-FZ10 made bySANYO Electric Co., Ltd., RC-10KW made by TOSHIBA CONSUMER MARKETINGCORPORATION, RZ-CG10J made by Hitachi Home & Life Solutions, Inc.,JKA-G100TG made by TIGER VACUUM BOTTLE CO LTD, NJ-GZ10-S made byMITSUBISHI ELECTRIC CORP and NHC-C10 made by ZOJIRUSHI CORP are used.Rice is cooked using rice cooking functions of the respective ricecookers, and it is confirmed whether or not rice can be cooked using therespective rice cookers. The result shows that all rice cookers can cookrice.

With respect to the impedance check frequencies (kHz) of theabove-mentioned rice cookers, the impedance check frequency of SR-XG10made by MATSUSHITA ELECTRIC IND CO LTD, the frequency of RC-10 KW madeby TOSHIBA CONSUMER MARKETING CORPORATION and RZ-CG10J made by HitachiHome & Life Solutions, Inc. are approximately 35 kHz, the frequency ofECJ-FZ10 made by SANYO Electric Co., Ltd. is approximately 30 kHz, thefrequency of NJ-GZ10-S made by MITSUBISHI ELECTRIC CORP and thefrequency of NHC-C10 made by ZOJIRUSHI CORP are approximately 40 kHz,and no oscillation is recognized with respect to JKA-G100TG made byTIGER VACUUM BOTTLE CO LTD.

Comparison Example 1

Heating of a container for an electromagnetic cooker and evaluation ofwhether or not the container can be heated by electromagnetic cookersare performed in the same manner as the experiment 1 except for that theconductive material of the comparison example 1 is formed of one sheetof aluminum foil having an outer diameter of φ145 mm.

Comparison Example 2

Heating of a container for an electromagnetic cooker and evaluation ofwhether or not the container can be heated by electromagnetic cookersare performed in the same manner as the experiment 1 except for that theconductive material of the comparison example 2 is formed of one sheetof aluminum foil having an outer diameter of φ150 mm.

From a result of the evaluation of the above-mentioned experiments, itis understood that the container for an electromagnetic cooker of thepresent invention can be heated corresponding to the electromagneticcooker of the respective manufacturers provided that the ratio ofresistance change and the ratio of inductance change fall withinallowable ranges. Further, with respect to the electromagnetic cookersmanufactured by the respective manufacturers, the smallest diameter ofthe pan which can be heated is 120 mm. However, by adjusting sizes ofthe conductive later such that the conductive layer satisfies theabove-mentioned change ratios as in the case of the experiment 3, thesmallest diameter of the container can be further decreased.

The high-frequency resistances (Ω), the inductances (μH), the ratios ofresistance change and the ratio of inductance change at the impedancecheck frequencies of the electromagnetic cookers manufactured by therespective manufacturers used in the experiments and at the impedancecheck frequencies of the containers for electromagnetic cookers of therespective experiments and the comparison examples and are shown inTable 1.

Further, configurations of the conductive materials for forming theconductive layers of the containers for electromagnetic cookers in therespective experiments and the comparison examples, and the evaluationresult of the respective experiments are shown in Table 2.

TABLE 1 Impedance check frequency (kHz) MATSUSHITA SANYO ELECTRICElectric TOSHIBA CM Hitachi HHL approximately approximatelyapproximately approximately MATSUSHITA SANYO TOSHIBA Hitachi 40 30 30 40ELECTRIC Electric CM HL high-frequency resistance (Ω) at inductance (μH)at impedance impedance check frequency check frequency Experiment 1 2.391.97 1.24 1.80 −18.22 −15.79 −9.42 −13.93 Experiment 2 2.43 1.98 1.271.83 −17.94 −15.11 −9.30 −13.67 Experiment 3 1.96 1.65 0.96 1.52 −13.70−12.45 −7.07 −10.21 Comparison 2.76 1.94 1.18 2.11 −10.50 −7.65 −4.49−8.05 example 1 Comparison 2.87 2.01 1.24 2.18 −11.30 −8.21 −4.86 −8.62example 2 MATSUSHITA SANYO TOSHIBA Hitachi MATSUSHITA SANYO TOSHIBAHitachi ELECTRIC Electric CM HL ELECTRIC Electric CM HL ratio ofresistance change at ratio of inductance change at impedance checkimpedance check frequency frequency [(R-R0)/R0] [(L-L0)/L0] Experiment 111.38 10.97 8.70 10.88 −0.30 −0.26 −0.23 −0.29 Experiment 2 11.57 10.988.92 11.11 −0.30 −0.25 −0.22 −0.28 Experiment 3 9.33 9.14 6.76 9.21−0.23 −0.20 −0.17 −0.21 Comparison 13.14 10.76 8.32 12.78 −0.17 −0.13−0.11 −0.16 example 1 Comparison 13.67 11.15 8.73 13.22 −0.19 −0.13−0.12 −0.18 example 2 Note: MATSUSHITA ELECTRIC: KZ-PH1 made byMATSUSHITA ELECTRIC IND CO LTD SANYO Electric: IC-SF10 made by SANYOElectric Co., Ltd. TOSHIBA CM: MR-A25LH made by TOSHIBA CONSUMERMARKETING CORPORATION Hitachi HR: MH-B1 made by Hitachi Home & LifeSolutions, Inc.

Note:

MATSUSHITA ELECTRIC: KZ-PH1 made by MATSUSHITA ELECTRIC IND CO LTDSANYO Electric: IC-SF10 made by SANYO Electric Co., Ltd.TOSHIBA CM: MR-A25LH made by TOSHIBA CONSUMER MARKETING CORPORATIONHitachi HR: MH-B1 made by Hitachi Home & Life Solutions, Inc.

TABLE 2 Configuration of conductive material Thickness of Outer diameterof Heating time Conductive material conductive conductive MATSUSHITASANYO TOSHIBA Configuration of conductive layer material (μm) material(mm) ELECTRIC Electric CM Hitachi HL Experiment 1 Laminated aluminumfoil 7 × 2 φ150 2′36″ 2′57″ 2′23″ 2′27″ Experiment 2 Laminated aluminumfoil 7 × 2 φ150 (inner 2′40″ 2′44″ 2′29″ 2′39″ doughnut shape diameter60) Experiment 3 Laminated aluminum foil 7 × 3 φ110 3′16″ 3′32″ 3′00″2′47″ doughnut shape (inner diameter 60) φ105 (inner diameter 60) φ100(inner diameter 60) Comparison Disk shape aluminum foil 7 φ145 4′43″Heating Heating Heating example 1 impossible impossible impossibleComparison Disk shape aluminum foil 7 φ150 4′39″ Heating Heating 3′48″example 2 impossible impossible Note: MATSUSHITA ELECTRIC: KZ-PH1 madeby MATSUSHITA ELECTRIC IND CO LTD SANYO Electric: IC-SF10 made by SANYOElectric Co., Ltd. TOSHIBA CM: MR-A25LH made by TOSHIBA CONSUMERMARKETING CORPORATION Hitachi HL: MH-B1 made by Hitachi Home & LifeSolutions, Inc.

Note:

MATSUSHITA ELECTRIC: KZ-PH1 made by MATSUSHITA ELECTRIC IND CO LTDSANYO Electric: IC-SF10 made by SANYO Electric Co., Ltd.TOSHIBA CM: MR-A25LH made by TOSHIBA CONSUMER MARKETING CORPORATIONHitachi HL: MH-B1 made by Hitachi Home & Life Solutions, Inc.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1 An explanatory view showing a method of measuring high-frequencyresistance and inductance using an impedance analyzer.

FIG. 2 A graph showing a result of measurement of the ratio ofresistance change with respect to the impedance check frequency of aconductive material and a ratio of inductance change with respect to theimpedance check frequency of the conductive material.

FIG. 3 A graph showing the relationship between the bulk specificresistance of a metal foil material and a foil thickness necessary forheating.

FIG. 4 A plan view showing an embodiment 1 of a container for anelectromagnetic cooker according to the present invention.

FIG. 5 A cross-sectional view taken along a line A-A in FIG. 4.

FIG. 6 A plan view showing an embodiment 2 of a container for anelectromagnetic cooker according to the present invention.

FIG. 7 A cross-sectional view taken along a line B-B in FIG. 6.

FIG. 8 A plan view of an inner cup in the embodiment 2 of the containerfor the electromagnetic cooker according to the present invention.

FIG. 9 A front view of the inner cup in the embodiment 2 of thecontainer for the electromagnetic cooker according to the presentinvention.

FIG. 10 A plan view of an embodiment 3 of a container for anelectromagnetic cooker according to the present invention.

FIG. 11 A cross-sectional view taken along a line C-C in FIG. 10.

FIG. 12 A cross-sectional view showing another embodiment of theembodiment 3 of the container for the electromagnetic cooker accordingto the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS AND SIGNS

-   1: container for electromagnetic cooker-   2: side wall-   3: bottom portion-   4: conductive layer-   5: conductive material-   6: non-conductive material-   7: content liquid convection hole

1. A container for an electromagnetic cooker including a conductivelayer at least in a bottom portion of the container made of anon-conductive material, wherein the ratio of resistance change(R−R0)/R0 of the conductive layer with respect to the impedance checkfrequency of a heating coil is set to 5.3 or more, and the ratio ofinductance change (L−L0)/L0 of the conductive layer with respect to theimpedance check frequency of the heating coil is set to −0.17 or less,wherein R indicates the high-frequency resistance on a heating coil sidewith a load, R0 indicates the high-frequency resistance on the heatingcoil side without a load, L indicates the inductance on the heating coilside with a load, and L0 indicates the inductance on the heating coilside without a load.
 2. A container for an electromagnetic cookeraccording to claim 1, wherein the conductive layer is formed of metalfoil.
 3. A container for an electromagnetic cooker according to claim 1,wherein the conductive layer is formed of a coating material containingmetal powder.
 4. A container for an electromagnetic cooker according toclaim 1, wherein the conductive layer is formed on an inner surface ofthe bottom portion of the container.
 5. A container for anelectromagnetic cooker according to claim 4, wherein the conductivelayer is made of a laminate material constituted of a conductivematerial and a non-conductive material, and the conductive material isdisposed on a bottom-portion side of the container.
 6. A container foran electromagnetic cooker according to claim 1, wherein thenon-conductive material of the conductive layer is curved upwardly alonga side wall of the container, and is adhered to a lower portion of aninner surface of the side wall of the container.
 7. A container for anelectromagnetic cooker according to claim 5, wherein a content liquidconvection hole is formed in the non-conductive material of the laminatematerial.
 8. A container for an electromagnetic cooker according toclaim 1, wherein the conductive layer is formed into a doughnut shape.9. A container for an electromagnetic cooker according to claim 1,wherein the conductive material of the conductive layer is formed intoan uneven shape for increasing a surface area of the conductivematerial.
 10. A container for an electromagnetic cooker according toclaim 7, wherein the conductive layer is configured to be verticallymovable.
 11. A container for an electromagnetic cooker according toclaim 1, wherein the conductive material is formed by lamination.
 12. Acontainer for an electromagnetic cooker according to claim 11, whereinthe conductive material is formed by lamination while preventing endportions of the conductive material from overlapping with each other.